1. Field of the Invention
The invention relates to an inductor and, more particularly, to an inductor adapted to be integrated with an integrated circuit (IC) chip by system-in-package (SIP) technology.
2. Description of the Prior Art
An inductor is a passive electrical component that can store energy in a magnetic field created by the electric current passing through it. An inductor's ability to store magnetic energy is measured by its inductance. Typically an inductor is a conducting wire shaped as a coil, the loops helping to create a strong magnetic field inside the coil due to Faraday's Law of Induction. Inductance is an effect resulting from the magnetic field that forms around a current-carrying conductor which tends to resist changes in the current. The number of loops, the size of each loop, and the material it is wrapped around all affect the inductance. For example, the magnetic flux linking these turns can be increased by coiling the conductor around a material with a high permeability such as ferrite magnetism.
So far there are various types of inductors disclosed in the prior arts. For example, a drum type of inductor is disclosed in Japanese patent No. 3-83909, another drum type of inductor is disclosed in U.S. Pat. No. 7,477,122, and a compact power semiconductor package with stacked inductor and integrated circuit die is disclosed in U.S. published application No. 20090160595. In general, most of the conventional inductors are integrated with an IC chip by two manners depicted in the following.
The first manner is that a lead is extended from a lower core of an inductor so as to be welded on a welding foot of a circuit board. However, in order to keep specific structure strength, the lower core must have a specific thickness, such that the total height of the inductor integrated with the IC chip will increase.
The second manner is that an external lead frame is connected under a lower core of an inductor so as to be welded on a lead frame of an IC chip. However, the height of the external lead frame will make the total height of the inductor integrated with the IC chip increase.
Thus, if the inductance has to be kept in a specific value, the total height of the conventional inductor integrated with the IC chip cannot be reduced, such that it cannot be adapted to a thin design.